As is known the art, in the human anatomy, the spine is a generally flexible column that can take tensile and compressive loads, allows bending motion and provides a place of attachment for ribs, muscles and ligaments. Generally, the spine is divided into three sections: the cervical, the thoracic and the lumbar spine. FIG. 1 illustrates schematically the lumbar spinal 1 and the sacrum regions 3 of a healthy, human spinal column. The sections of the spine are made up of individual bones called vertebrae and the vertebrae are separated by intervertebral discs which are situated therebetween.
FIG. 2 illustrates a portion of the right side of a lumbar spinal region with a healthy intervertebral disc 5 disposed between two adjacent vertebrae 7, 9. In any given joint, the top vertebra may be referred to as the superior vertebra and the bottom one as the inferior vertebra. Each vertebra comprises a generally cylindrical body 7a, 9a, which is the primary area of weight bearing, and three bony processes, e.g., 7b, 7c, 7d (two of which are visible in FIG. 2). As shown in FIG. 7A, in which all of the processes are visible, processes 7b, 7c, 7d extend outwardly from vertebrae body 7 at circumferentially spaced locations. The processes, among other functions, provide areas for muscle and ligament attachment. Neighboring vertebrae may move relative to each other via facet components 7e (FIG. 2), which extend from the cylindrical body of the vertebrae and are adapted to slide one over the other during bending to guide movement of the spine. There are two facet joints, each defined by upper and lower facet components, associated with adjacent vertebra. A healthy intervertebral disc is shown in FIG. 3. As shown in FIG. 3, an intervertebral disc has 4 regions: a nucleus pulposus 11, a transition zone 13, an inner annulus fibrosis region 15 and an outer annulus fibrosis 17. Generally, the inner annulus fibrosis region 15 and the outer annulus fibrosis region 17 are made up of layers of a fibrous gristly material firmly attached to the vertebral bodies above and below it. The nucleus pulposus 11 is typically more hydrated in nature.
These intervertebral discs function as shock absorbers and as joints. They are designed to absorb the compressive and tensile loads to which the spinal column may be subjected while at the same time allowing adjacent vertebral bodies to move relative to each other a limited amount, particularly during bending (flexure) of the spine. Thus, the intervertebral discs are under constant muscular and/or gravitational pressure and generally are the first parts of the lumbar spine to show signs of “wear and tear”.
Facet joint degeneration is also common because the facet joints are in almost constant motion with the spine. In fact, facet joint degeneration and disc degeneration frequently occur together. Generally, although one may be the primary problem while the other is a secondary problem resulting from the altered mechanics of the spine, by the time surgical options are considered, both facet joint degeneration and disc degeneration typically have occurred. For example, the altered mechanics of the facet joints and/or intervertebral disc may cause spinal stenosis, degenerative spondylolisthesis, and degenerative scoliosis.
One surgical procedure for treating these conditions is spinal arthrodesis (i.e., spine fusion), which has been performed both anteriorally and/or posteriorally. The posterior procedures include in-situ fusion, posterior lateral instrumented fusion, transforaminal lumbar interbody fusion (“TLIF”) and posterior lumbar interbody fusion (“PLIF”). Solidly fusing a spinal segment to eliminate any motion at that level may alleviate the immediate symptoms, but for some patients maintaining motion may be advantageous. It is also known to surgically replace a degenerative disc or facet joint with an artificial disc or an artificial facet joint, respectively. However, none of the known devices or methods provide the advantages of the embodiments of the present disclosure.
Accordingly, the foregoing shows there is a need for an improved spinal arthroplasty that avoids the drawbacks and disadvantages of the known implants and surgical techniques.